Systematical shape evolution of hexagonal NiSe crystals caused by mixed solvents and ammonium chloride

Systematic shape evolution of hexagonal NiSe crystals is realized via a simple solvothermal route in a mixture of NiCl2·6H2O, elemental selenium, hydrazine hydrate and ethylenediamine. By introducing ammonium chloride as electrolyte and varying the volume ratios of hydrazine hydrate to ethylenediamine, shape evolution of hexagonal NiSe crystals from small hexagonal microdisks to hexagonal microdisks in larger width, microspheres, hexagonal prisms and hexagonal bitowers is successfully achieved. X-ray powder diffraction, field emission scanning electron microscopy, energy dispersion spectrometer, transmission electron microscopy and selected area electron diffraction are performed for the analyses of the products. The ionization and hydrolysis of ammonium chloride decrease the nucleation rate of hexagonal NiSe and the diffusion rate of growth resources, while the adsorption of ethylenediamine at {001} facets of hexagonal NiSe crystals inhibits the crystal growth in <001> directions, thus leading to various novel architectures.